Method and system for low complexity conjugate gradient based equalization in a wireless system

ABSTRACT

Methods and systems for processing signals in a receiver are disclosed herein and may include updating a plurality of filter taps utilizing at least one channel response vector and at least one correlation vector, for a plurality of received clusters, based on initialized values related to the at least one channel response vector and the at least one correlation vector. At least a portion of the received signal clusters may be filtered utilizing at least a portion of the updated plurality of filter taps. The update may be repeated whenever a specified signal-to-noise ratio (SNR) for the received signal clusters is reached. The initialized values may be updated during a plurality of iterations, and the update may be repeated whenever a specified number of the plurality of iterations is reached.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

The present application is a continuation of U.S. application Ser. No.13/192,773, filed Jul. 28, 2011, which is a continuation of U.S.application Ser. No. 12/940,150, filed on Nov. 5, 2010, which is acontinuation of U.S. application Ser. No. 11/565,365, filed on Nov. 30,2006, which is a continuation-in-part of application Ser. No.11/173,502, filed on Jun. 30, 2005, which claims priority to provisionalApplication No 60/616,895, filed on Oct. 6, 2004. The above-referencedUnited States patent applications are all hereby incorporated herein byreference in their entirety. This application is also related to thefollowing applications, each of which is incorporated herein byreference in its entirety:

-   U.S. patent application Ser. No. 11/565,381 filed on Nov. 30, 2006;-   U.S. patent application Ser. No. 11/173,870 filed on Oct. 6, 2004;-   U.S. patent application Ser. No. 11/174,303 filed on Oct. 6, 2004;-   U.S. patent application Ser. No. 11/173,502 filed on Oct. 6, 2004;    and-   U.S. patent application Ser. No. 11/173,854 filed on Oct. 6, 2004.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to processing receivedwireless signals. More specifically, certain embodiments of theinvention relate to a method and system for low complexity conjugategradient based equalization in a wireless system.

BACKGROUND OF THE INVENTION

In most current wireless communication systems, nodes in the network maybe configured to operate based on a single transmit and a single receiveantenna. However, for many current wireless systems, the use of multipletransmit and/or receive antennas may result in an improved overallsystem performance. These multi-antenna configurations, also known assmart antenna techniques, may be utilized to reduce the negative effectsof multipath and/or signal interference may have on signal reception.Existing systems and/or systems which are being currently deployed, forexample, code division multiple access (CDMA) based systems, timedivision multiple access (TDMA) based systems, wireless local areanetwork (WLAN) systems, and orthogonal frequency division multiplexing(OFDM) based systems, such as IEEE 802.11 a/g, may benefit fromconfigurations based on multiple transmit and/or receive antennas. It isanticipated that smart antenna techniques may be increasingly utilizedboth in connection with the deployment of base station infrastructureand mobile subscriber units in cellular systems to address theincreasing capacity demands being placed on those systems. These demandsarise, in part, from the shift underway from current voice-basedservices to next-generation wireless multimedia services that provideintegrated voice, video, and data transmission.

The utilization of multiple transmit and/or receive antennas is designedto introduce a diversity gain and to suppress interference generatedwithin the signal reception process. Such diversity gains improve systemperformance by increasing received signal-to-noise ratio, by providingmore robustness against signal interference, and/or by permittinggreater frequency reuse for higher capacity. In communication systemsthat incorporate multi-antenna receivers, a set of M receive antennasmay be utilized to null the effect of M−1 interferers. Accordingly, Nsignals may be simultaneously transmitted in the same bandwidth using Ntransmit antennas, with the transmitted signal then being separated intoN respective signals by way of a set of N antennas deployed at thereceiver.

This type of systems may be referred to as multiple-inputmultiple-output (MIMO) systems. One attractive aspect of multi-antennasystems, in particular MIMOs, is the significant increase in systemcapacity which may be achieved by utilizing these transmissionconfigurations. For a fixed overall transmitted power the capacityoffered by a MIMO configuration may scale with the increasedsignal-to-noise ratio (SNR). For example, in the case of fadingmultipath channels, a MIMO configuration may increase system capacity bynearly M additional bits/cycle for each 3-dB increase in SNR.

However, the widespread deployment of multi-antenna systems in wirelesscommunications, particularly in wireless handset devices, has beenlimited by the increased cost that results from the increased size,complexity, and power consumption. Providing a separate RF chain foreach transmit and receive antenna is a direct factor in the increasedthe cost of multi-antenna systems. Each RF chain generally comprises alow noise amplifier (LNA), a filter, a downconverter, and ananalog-to-digital converter (A/D). In certain existing single-antennawireless receivers, the single required RF chain may account for over30% of the receiver's total cost. It is therefore apparent that as thenumber of transmit and receive antennas increases, the systemcomplexity, power consumption, and overall cost may increase.

Furthermore, multi-path propagation in band-limited time dispersivechannels may cause inter-symbol interference (ISI), which has beenrecognized as a major obstacle in achieving increased digitaltransmission rates with the required accuracy. ISI may occur when thetransmitted pulses are smeared out so that pulses that correspond todifferent symbols are not discernable or separable. Meanwhile, datareceived from a desired user may be disturbed by other transmitters, dueto imperfections in the multiple access scheme, giving rise tointer-carrier interference (ICI). For a reliable digital transmissionsystem, it is desirable to reduce the effects of ISI and ICI.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of ordinary skill in the artthrough comparison of such systems with the present invention as setforth in the remainder of the present application with reference to thedrawings.

BRIEF SUMMARY OF THE INVENTION

A system and method for low complexity conjugate gradient basedequalization in a wireless system, substantially as shown in and/ordescribed in connection with at least one of the figures, as set forthmore completely in the claims.

Various advantages, aspects and novel features of the present invention,as well as details of an illustrated embodiment thereof, will be morefully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary spatial multiplexing (SM)multiple-input multiple-output (MIMO) antenna system utilizing aconjugate gradient taps optimizer, in accordance with an embodiment ofthe invention.

FIG. 2 is a block diagram of a radio frequency (RF) processing blockthat may be utilized in accordance with an aspect of the invention.

FIG. 3 is a block diagram of a receiver front end of atwo-transmit-two-receive MIMO antenna system utilizing conjugategradient optimization, in accordance with an embodiment of theinvention.

FIG. 4 is a block diagram of a receiver front end of amultiple-transmit-multiple-receive MIMO antenna system utilizingconjugate gradient optimization, in accordance with an embodiment of theinvention.

FIG. 5 is a flow diagram illustrating exemplary steps for processingsignals in a receiver, in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor low complexity conjugate gradient based equalization in a wirelesssystem and may comprise updating a plurality of filter taps of theequalizing filter utilizing at least one channel response vector, and atleast one correlation vector, for a plurality of received clusters. Theupdating of the equalizing filter taps may be based on initializedvalues related to the channel response vector and the correlationvector. At least a portion of the received signal clusters may befiltered utilizing at least a portion of the updated plurality of filtertaps. A signal cluster may be defined as plurality of signals that aresampled and synchronized with the receiver chip-rate clock (or fractionof chip-rate period). Each sample constitutes an estimate of thereceived signal that propagated a different path (channel). The updatemay be repeated whenever a specified signal-to-noise ratio (SNR) for thereceived signal clusters is reached. The initialized values may beupdated during a plurality of iterations, and the update may be repeatedwhenever a specified number of the plurality of iterations is reached. Aplurality of chip-rate synchronously sampled signals may be generatedutilizing the plurality of received clusters and/or a chip clockingsignal. The correlation vector may be generated utilizing the pluralityof chip-rate synchronously sampled signals, and may comprise complexconjugates of a plurality of chip-rate synchronously sampled signals.The plurality of chip-rate synchronously sampled signals may begenerated based on the plurality of received clusters. The channelresponse vector and the correlation vector may be updated based on aminimum-mean-square-error (MMSE) algorithm. An estimate of the pluralityof received clusters may be generated based on the filtering.

FIG. 1 is a block diagram of an exemplary spatial multiplexing (SM)multiple-input multiple-output (MIMO) antenna system utilizing aconjugate gradient taps optimizer, in accordance with an embodiment ofthe invention. Referring to FIG. 1, there is shown a transceiver system120 that may comprise a baseband transmit station (BTS) BTS1, aplurality of receive antennas 128 _(1 . . . Nr), a plurality of radiofrequency (RF) receive blocks 132 _(1 . . . Nr) a plurality of chipmatched filters (CMF) 134 _(1 . . . Nr), a plurality of cluster pathprocessors (CPP) 136 _(1 . . . Nr), and a baseband processor 138.

On the transmit side, the baseband transmit station BTS1 may comprisepre-coding phase and/or amplitude alignment block 121, N_(t) number ofRF transmit blocks 124 _(1 . . . Nt), and N number of antennas 126_(1 . . . Nt) for the BTS1. The BTS1 may transmit one or more spatiallymultiplexed signals over channels having actual time varying impulseresponses. The total time varying impulse response 127 of all receiveand transmit channels utilized within the transceiver system 120 maycorrespond to the channel matrix HH. In one aspect of the invention, theBTS1 may utilize spatial multiplexing techniques to transmit one or moresignals utilizing the transmit antennas 126 _(1 . . . Nt) whichcorrespond to BTS1. However, the invention may not be limited in thisregard. For example, the transmit side may comprise additional basebandtransmit stations and one or more antennas from other BTSs may beutilized during the same transmission of the spatially multiplexedsignal. Or alternatively, the BTS1 may utilize transmit diversitytechniques to transmit one or more signals utilizing a—coding phaseand/or amplitude alignment block 121 and the transmit antennas 126_(1 . . . Nt).

The RF transmit blocks 124 _(1 . . . Nt) may comprise suitable logic,circuitry, and/or code that may be adapted to process an RF signal. TheRF transmit blocks 124 _(1 . . . Nt) may perform, for example,filtering, amplification, and/or analog-to-digital (A/D) conversionoperations. The plurality of transmit antennas 126 _(1 . . . Nt) maytransmit the processed RF signals from the plurality of RF transmitblocks 124 _(1 . . . Nt) to a plurality of receive antennas 128_(1 . . . Nr).

The plurality of RF receive blocks 132 _(1 . . . Nr) may comprisesuitable logic, circuitry and/or code that may be adapted to amplify andconvert the received analog RF signals R_(1 . . . Nr) down to basebandfrequency. The plurality of RF receive blocks 132 _(1 . . . Nr) may eachcomprise an analog-to-digital (A/D) converter that may be utilized todigitize the received analog baseband signal, as well as voltagecontrolled oscillator, a mixer, and/or a low pass filter.

The plurality of chip matched filters (CMF) 134 _(1 . . . Nr) maycomprise suitable logic, circuitry, and/or code that may be adapted tofilter outputs of the plurality of RF receive blocks 132 _(1 . . . Nr)so as to produce in-phase (I) and quadrature (Q) components. In thisregard, in an embodiment of the invention, the plurality of chip matchedfilters (CMF) 134 _(1 . . . Nr) may comprise a pair of digital filters,for example, that may be adapted to filter the I and Q components towithin the bandwidth of WCDMA baseband, for example 3.84 MHz.

The plurality of cluster path processors (CPP) 136 _(1 . . . Nt) may beadapted to generate a plurality of Nr×Nt channel estimates of the actualtime varying impulse responses. A CPP_(i) (i=1 . . . Nt) generates thechannel estimates Ĥ_(Ii), . . . Ĥ_(Nri) received at antennasR_(1 . . . Nr). The baseband processor 138 may be adapted to receive aplurality of in-phase (I_(i)) and quadrature (Q_(i)) are components ofX_(i) (i=1 . . . N_(r)) Output from the plurality of chip-matchedfilters (CMF) 134 _(1 . . . Nr). Block 138 also receives the estimatesĤ_(1i), . . . Ĥ_(Nri). The baseband processor 138 may then generate aplurality of estimates {circumflex over (X)}₁ to {circumflex over(X)}_(P) of the original input signals X₁ to X_(P) per baseband transmitstation.

In operation, the transceiver system 120 may receive wireless signals,which may be distorted due to fading effect and other distortingphenomena. In this regard, the baseband processor 138 may utilize signalequalizing, or filtering, to reverse the effect of the communicationchannel or media interferences. In an exemplary embodiment of theinvention, the baseband processor 138 may also comprise one or moreconjugate gradient taps optimizer blocks (CGTO) 150 and one or moreequalizers 152. The CGTO 150 may comprise suitable circuitry, logicand/or code and may utilize a conjugate gradient-based algorithm tocalculate one or more equalizer filter tap settings. The calculatedequalizer taps may be used by the equalizer 152 to equalize or filterthe received signal estimate. The equalizer 152 may also update an errorfunction at a given rate, while the conjugate gradient-based algorithmin the CGTO 150 may continuously iterate, for example a plurality ofcycles for each update, so that the equalizer taps may be updated andoptimized by the CGTO 150 for the received wireless signal. In anotherembodiment of the invention, the algorithm used by the CGTO 150 may bebased on a Minimum Mean Square Error (MMSE) algorithm. In this regard,the CGTO 150 may utilize a reduced number of calculation cycles, forexample by eliminating matrix-vector multiplication, which may result inincreased processing time and reduced implementation costs.

FIG. 2 is a block diagram of a radio frequency (RF) processing blockthat may be utilized in accordance with an aspect of the invention.Referring to FIG. 2, the RF processing block 200 may comprise suitablelogic, circuitry, and/or code and may be adapted to amplify and convertthe received analog RF signal down to baseband and then digitize it. Inan exemplary aspect of the invention, the RF processing block 200 maycomprise an LNA 204, a voltage controlled oscillator (VCO) 208, a mixer206, a low pass filter (LPF) 212, and an analog-to-digital converter(A/D) 213. The LNA 204 may be adapted to receive an RF signal 202 andamplify it based on a determined gain level. The VCO 208 may comprisesuitable logic, circuitry, and/or code and may be adapted to output asignal of a specific frequency, which may be pre-determined, orcontrolled, by a voltage signal input to the VCO. The VCO signal 210 maybe mixed by the mixer 206 with the amplified signal received from theLNA 204. The LPF 212 may comprise suitable logic, circuitry, and/or codeand may be adapted to receive the mixed signal from the mixer 206. Thefrequencies of the mixed signal may be limited by the LPF 212 to adetermined range of frequencies up to a certain upper frequency limit,and the LPF 212 may output that range of frequencies as a basebandsignal to the A/D 213. The A/D converter 213 may comprise suitablelogic, circuitry, and/or code that may be adapted to receive the limitedanalog baseband signal from the LPF 212 and output a digital signal 214,which may sample the analog signal at a pre-defined rate.

FIG. 3 is an exemplary block diagram described in FIG. 1. It shows theblock diagram of a receiver front end of a two-transmit-two-receive(Nt=2; Nr=2) MIMO antenna-system utilizing conjugate gradientoptimization, in accordance with an embodiment of the invention.Referring to FIG. 3, there is illustrated a receiver front endcomprising cluster path processors CPP1 302 and CPP2 304, a correlatorblock 306, CGTO blocks 308 and 310, and equalizer blocks 312 and 314.

The CPPs 302 and 304 may comprise suitable circuitry, logic and/or codeand may enable the generation of the channel estimates (Ĥ₁₁, Ĥ₁₂, Ĥ₂₁,Ĥ₂₂). A designated CPP named Master CCP (302) provides the chip-rate (ormultiple chip-rate) clocking signal to the entire receiver. Itfacilitates the removing of the time-tracking circuitry from all theother CPP's and the generation of timely synchronous outputs (thechannels estimates) from all the CPP's. Furthermore, the Master CPP(302) receives signals from each CPP (304) that indicate the strength ofthe aggregate channels (for example, measured by the mean power of allchannels) and the aggregate time position—of the channelsprocessed—relative to the Master CPP clocking signal. The Master CPP(302) is equipped with circuitry/software that facilitates aclocking-signal that tracks the aggregate received timing and powersignals from all CPP's in a manner and accuracy that is required. Inthis respect the connection 303—between the Master CPP 302 and CPP304—facilitates the flow of time, power signals, and may include otherinformation, to the Master CPP. Block 302, also, outputs the timingsignals, through 303, to the entire receiver. The channel responseestimates (Ĥ₁₁, Ĥ₁₂, Ĥ₂₁, Ĥ₂₂) 320, 328, 322, 330 and the signals X′1324 and X′2 326—from CPPs 302 and 304—may be fully synchronized in asense of being sampled by a single clock.

The correlator block 306 may comprise suitable circuitry, logic and/orcode and may enable generation of correlation vectors 332 and 334 of thetwo receive antennas, based on the generated chip-rate synchronouslysampled signals X′1 326 and X′2 324 received from the time-master CPP302. The correlation vectors 332 may comprise correlations R11 and R12,and correlation vectors 334 may comprise correlations R21 and R22.

The CGTO blocks 308 and 310 may comprise suitable circuitry, logicand/or code and may enable generating and updating of equalizer tapvalues 336, . . . , 342, based on, for example, a conjugategradient-based algorithm. The generated equalizer tap values 336, . . ., 342 may be communicated to the equalizer blocks 312 and 314 forfurther processing.

The equalizer blocks 312 and 314 may comprise suitable circuitry, logicand/or code and may generate received signal estimates 344 and 346 basedon the generated chip-rate synchronously sampled signals X′1 326 and X′2324 and the updated equalizer taps 336, . . . , 342.

In operation, the CPPs 302 and 304 may receive input signal X1 316 froma first antenna, and input signal X2 318 from a second antenna. Thereceived signals 316 and 318 may have been transmitted from two transmitantennas. The CPP 302 may generate channel responses Ĥ₁₁ 320 and Ĥ₂₁322, based on received wireless signals X1 316 and X2 318 received viatwo receive antennas. The received signals may be represented as X_(r)(r=1:2). The CPP 304 may generate channel responses Ĥ₁₂ 328 and Ĥ₂₂ 330,also based on input wireless signals X1 316 and X2 318. Each channelresponse Ĥ_(ri) (i=1:2, r=1:2) may comprise a vector of N_(CH) taps,where N_(CH) may comprise the delay spread of the channel. The generatedchannel responses Ĥ₁₁ 320 and Ĥ₂₁ 322 may be communicated to CGTO 308,and the generate channel responses Ĥ₁₂ 328 and Ĥ₂₂ 330 may becommunicated to the CGTO 310.

The coming signal may be transmitted through two transmit antennas andmay be received by two receiver antennas first, and then may beprocessed by two CPP's (Cluster Path Processes) 302 and 304. Each CPP-i(i=1,2) 302, 304 may generate a plurality of channel response—Ĥ_(ri)(r=1:2) 320, 322, 328, 330 of the desired signal, where each channelresponse may comprise a vector of Nch taps, and Nch may be the delayspread of the channel.

As explained before, the CPP 302 may be defined as the time-master CPPand may be utilized to receive timing signals from all the other CPP'sand may generate the chip clocking signal. This chip clock or other timesignal, which may comprise multiple chip clock-time, may be used tosample the input signals Xr (r=1:2) 316, 318, creating the output X1′316 and X2′ 318 and the channel responses—Ĥ_(ri) (r=1:2; i=1:2) 320,322, 328, 330, as well as other generated signals. The received signalsXr (r=1:2) 316, 318 that clocked at chip rate may be further processedin the correlate-generator 306 block that may generate the vector set ofcorrelations {Rr1,r2} 332, 334. Each vector Rr1,r2 (r1=1:NR; r2=1:NR)may comprise the correlation taps that are given by the followingequation:Rr1,r2(n)=E{Xr1·X*r1−n},where n=0:Nch-1 and “*” is the complex conjugate.

The correlation set {Rr1,r2(n);} 332, 334 together with the set ofchannel responses vectors Ĥ_(ri) (r=1:2; i=1:2) 320, 322, 328, 330 maybe input into the CG-i (i=1:2) 308, 310 that may generate the equalizertaps (w_cg). The taps may be updated according to changes in the channelestimates the SNR and other conditions described within the context ofthis invention.

The CG tape-optimizer blocks 308, 310 may utilize the CG algorithmdescribed herein below as well as with regard to FIG. 5, and may useMMSE criteria, for example. One or more modifications related to thisalgorithm may also be utilized, such as initialization/re initializationblock, control block for the number of iteration, and/or block thatestimates the convergence status.

In an exemplary embodiment of the invention, the CGTO blocks 308 and 310may utilize a conjugate gradient-based (CG) algorithm for generating andupdating the equalizer taps 336, . . . , 342. The CG algorithm may beexpressed by the following pseudo code:

STEP 1 If initialization_flag alf   = alf_0 bet   = bet_0 w_cg =zeros(2*M,1); end STEP 2 If updating_clk  r = h;  p  = r;  R = R_in; endSTEP 3 If Iteration_clk & iteration_flg Rp = R*p; r_curr = r′*r; pRp =p′*Rp; w_cg = w_cg + alf*p; r = h − R*w_cg; p = r + bet*p;  nm_iter =nm_iter + 1; end STEP 4 snr_cg = Get_CG_SNR(w_cg, H); STEP 5 if (snr_cg<snr_0) & (iter_flag == 0) w_cg = h; iter_ flag = 1; nm_iter = 0; elseifsnr_cg <snr_1 if nm_iter < N_iterations update alf; update bet; elseiteration_flg = 0; end end

During an exemplary equalizer tap calculation in accordance with theabove algorithm, at step 1, the algorithm parameters alf and bet may beinitialized to alf_0 and bet_0. The initial desired solution w_cg mayalso be initialized to a zero-vector. The algorithm parameters alf andbet may be expressed by the following equations:alf _(k) =r ^(T) _(k-1) ·r _(k-1) /p ^(T) _(k-1) Rp _(k-1); andbet _(k) =p ^(T) _(k-1) A r _(k-1) /p ^(T) _(k-1) Rp _(k-1),where r_(k) may comprise a vector of dimension N, calculated at thek^(th) iteration, p_(k) may comprise a vector of the same dimension,calculated at the k^(th) iteration, and R may comprise an array of N×Ndimension. Therefore, each calculation iteration may utilize N²+3×Nmultiplications and 2 division operations. In this regard, calculationcomplexity of the CG algorithm may be significantly reduced bypresetting values alf_0 and bet_0 to the alf and bet parameters. Thealf_0 and bet_0 values may be pre-calculated and used in the CGalgorithm. In addition, the values may be dynamically exchanged duringexecution of the CG algorithm, based on pre-defined conditions. Forexample, such pre-defined conditions may be characterized by theSignal-to-Noise-Ratio (SNR). For example, the algorithm parameters alfand bet may be associated with a range of SNR values that may bemeasured during signal reception, and the algorithm parameters alf andbet may be reset if such SNR value is achieved. In other instances, thealgorithm parameters alf and bet may be set to a desired value, whichmay be determined in offline testing.

During step 2 of the CG algorithm, the external conditions may beupdated. In this regard, the channel response vectors H11, H12, H21, andH22 (represented by h), as well as the correlations vectors r11, r12,r21, and r22 (represent by Rin) may be input. During step 3, oneiteration of the CG algorithm may be performed, if the number ofiteration is less than the value N_iteration. During step 4, evaluationof the equalizer taps may be performed by calculating the SNR value.During step 5, the estimated SNR decisions related to a subsequent cyclemay take place. The value snr_0 may represent a level of signal/noisewhen the algorithm may be ineffective and therefore may not be used. Thevalue snr_1 may define a higher level SNR where the improvement toperformance may be diminishing and therefore the algorithm may not beapplied. In this regard, the CG algorithm may be effective for a rangeof SNR values.

For example, if snr<snr_0, the CG algorithm may output h and theequalizer blocks 312 and 314 may operate as maximum ratio combiners. TheCG algorithm may then be initialized to new iteration sets. If snr<snr_1and if the number of iteration performed is less than N_iteration,another cycle of the CG algorithm may be performed. Otherwise, the CGalgorithm may halt until the next updating cycle. Within a given SNRrange, the number of cycles N that the CG algorithm may be applied maybe deduced. The CG algorithm, however, may not be limited to anypre-defined range of SNR values. Consequently, the algorithm parametersN, alf, and bet may be determined for a plurality of SNR ranges. It isknown, to one skilled in the art, that the chosen N—the dimension (thenumber of taps) of w_cg the equalizer filters may be at the range oftwice to four time the delay spread (measured in number of chips—N_(ch)that defines the channel response). However the calculated correlationvectors r11, r12, r21, and r22 (Also called R11, R12, R21 and R22 andare the outputs 334 and 332) may be limited to the delay spread N_(CH).The assigning the correlation vectors to larger vectors the non definedvalue are replaced with zeros. The implementation of this invention,therefore, may include limitation on the calculation of the innerproducts, between two vectors, to only non zero values and thereforereducing the calculation and the complexity load.

FIG. 4 is a block diagram of a receiver front end of amultiple-transmit-multiple-receive MIMO antenna system utilizingconjugate gradient optimization, in accordance with an embodiment of theinvention. It is the architecture in the general case of Nt transmittersor antennas and Nr receivers. Referring to FIG. 4, there is illustrateda receiver front end comprising cluster path processors CPP_(1 . . . Nr)402, . . . , 404, a correlator block 406, CGTO blocks 408, . . . , 410,and equalizer blocks 412, . . . , 414. The input wireless signals 416, .. . , 418 may be transmitted by Nt transmit antennas and received by Nrreceive antennas.

In operation, the CPPs 402, . . . , 404 may receive input signals 416, .. . , 418 Xr (r=1:Nr) via Nr receive antennas. The CPPs 402, . . . , 404may generate channel responses H_(r,i) (r=1:Nr; i=1:Nt) based on thereceived wireless signals 416, . . . , 418. Each channel responseH_(r,i) may comprise a vector of N_(CH) taps, where N_(CH) may comprisethe delay spread of the channel. The generated channel responses 420, .. . , 422 H_(r,i) (r=1:Nr; i=1:Nt) may be communicated to CGTO blocks408, . . . , 410.

The CPP 402 may receive a plurality of timing signals 403 from eachremaining CPP, and may generate chip-rate synchronously sampled signalsX_(1 . . . Nr) 424, based on the input signals 416, . . . , 418. Thechip-rate synchronously sampled signals X_(1 . . . Nr) 424 may becommunicated to the correlator block 406. The correlator block 406 maygenerate vector set of correlation values {R_(r1, r2)} 426 of the Nrreceive antennas, based on the generated chip-rate synchronously sampledsignals X_(1 . . . Nr) 424 received from the time-master CPP 402. Thevector set of correlations {R_(r1,r2)} 426 may comprise individualvectors. Each individual vector R_(r1,r2) (r1=1:Nr, r2=1:Nr) maycomprise correlation taps which may be represented by the followingequation:R _(r1,r2)(n)=E{X _(r1) ·X* _(r2-n)},where n=0:N_(ch)-1 and “*” may represent a complex conjugate. Thecorrelation set {R_(r1,r2)(n)} 426 and the set of channel responsesvectors H_(r,i) (r=1:Nr; i=1:Nt) may be communicated to the CGTO blocks408, . . . , 410. The CGTO blocks 408, . . . , 410 may generate theequalizer taps 428, . . . , 430 for the equalizer blocks 412, . . . ,414, and may continuously update them. The equalizer blocks 412, . . . ,414 may generate received signal estimates 432, . . . , 434 based on thegenerated chip-rate synchronously sampled signals X_(1 . . . Nr) 424 andthe updated equalizer taps 428, . . . , 430.

FIG. 5 is a flow diagram illustrating exemplary steps for processingsignals in a receiver, in accordance with an embodiment of theinvention. Referring to FIG. 5, there is shown a flow diagram of theexemplary CG algorithm, as described above with regard to FIG. 3. Theexemplary steps may begin at step 502. At 504, the algorithm parametersalf and bet may be initialized to pre-determined values. The weightedconjugate gradient (WCG) value may be reset to zero. At 506, thealgorithm parameter r may be updated with channel impulse responses, andalgorithm parameter R_(in) may be updated with correlation vectorvalues. At 508, a single iteration may be performed by the CG algorithmand WCG may be calculated.

At 510, a signal-to-noise ratio (SNR) may be calculated. At 514, it maybe determined whether the calculated SNR is less than snr_0. IfSNR<snr_0, then at 512, WCG may be determined as h, and the determinedWCG may be output. The algorithm may then resume at step 502. If SNR isnot less than snr_0, at 516, it may be determined whether SNR<snr_1. IfSNR is not less than snr_1, the algorithm may reset and start again atstep 502. If SNR<snr_1, at 520, it may be determined whether the numberof performed iterations is less than the value of N_iterations. If thenumber of performed iterations is less than the value of N_iterations,at 518, the algorithm parameters alf and bet may be updated. Thealgorithm may then reset and continue at step 502. If the number ofperformed iterations is not less than the value of N_iterations, at 522,the current algorithm cycle may be stopped and no WCG value may beoutput. The CG algorithm may then reset and continue at step 502.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A method for processing wireless signals,comprising: receiving first and second wireless signals comprisinginformation transmitted from one or more transmit antennas; generating acorrelation vector that corresponds to said first wireless signalcorrelated with a complex conjugate of said second wireless signal; andupdating an equalizer tap according to said correlation vector upondetermining that a signal-to-noise ratio (SNR) requirement is satisfied.2. The method of claim 1, further comprising generating said equalizertap according to a channel response vector that corresponds to thecombination of a receive antenna and a transmit antenna.
 3. The methodof claim 1, wherein said equalizer tap is updated iteratively while theSNR requirement is satisfied.
 4. The method of claim 1, wherein saidequalizer tap is updated a pre-determined number of times.
 5. The methodof claim 1, further comprising generating a chip-rate synchronouslysampled signal based on a chip clocking signal and at least one of saidfirst and second wireless signals.
 6. The method of claim 5, furthercomprising generating a received signal estimate based on said generatedchip-rate synchronously sampled signal.
 7. The method of claim 5,wherein the correlation vector is generated using the chip-ratesynchronously sampled signal.
 8. The method of claim 1, wherein saidfirst and second wireless signals comprise a signal cluster.
 9. Themethod of claim 1, wherein said equalizer tap is updated according to aconjugate gradient based on said correlation vector.
 10. The method ofclaim 1, wherein said SNR requirement is determined to be satisfied whensaid SNR falls within a predetermined range.
 11. A system for processingwireless signals, comprising: one or more receive ports configured toreceive first and second wireless signals comprising informationtransmitted from one or more transmit antennas; a correlator configuredto generate a correlation vector that corresponds to said first wirelesssignal correlated with a complex conjugate of said second wirelesssignal; and a conjugate gradiant tap optimizer (CGTO) configured toupdate an equalizer tap according to said correlation vector upondetermining that a signal-to-noise ratio (SNR) requirement is satisfied.12. The system of claim 11, wherein said CGTO is configured to generatesaid equalizer tap according to a channel response vector thatcorresponds to the combination of a receive antenna and a transmitantenna.
 13. The system of claim 11, wherein said CGTO is configured toupdate said equalizer tap iteratively while the SNR requirement issatisfied.
 14. The system of claim 11, wherein said CGTO is configuredto update said equalizer tap a pre-determined number of times.
 15. Thesystem of claim 11, wherein said correlator is configured to generate achip-rate synchronously sampled signal based on a chip clocking signaland at least one of said first and second wireless signals.
 16. Thesystem of claim 15, wherein said correlator is configured to generate areceived signal estimate based on said generated chip-rate synchronouslysampled signal.
 17. The system of claim 15, wherein said correlator isconfigured to generate said correlation vector using the chip-ratesynchronously sampled signal.
 18. The system of claim 11, wherein saidfirst and second wireless signals comprise a signal cluster.
 19. Thesystem of claim 11, wherein said CGTO is configured to update saidequalizer tap according to a conjugate gradient based on saidcorrelation vector.
 20. The method of claim 11, wherein said CGTO isconfigured to determine that said SNR requirement is satisfied when saidSNR falls within a predetermined range.